This invention relates to an internal combustion engine and more particularly to an improved cylinder head porting and fuel injection arrangement for multi-valve engines.
It is well known that the performance of an engine is quite dependent upon the configuration and functioning of its induction system. However, the requirements of the induction system vary significantly as the running condition of the engine varies. At low speeds and at idle it is desirable to have the intake charge enter the combustion chamber at a relatively high velocity and in a pattern which will effect turbulence in the combustion chamber.
This turbulence is desirable in order to ensure rapid flame propagation which is necessary for complete combustion. In addition, it may be desirable to provide an arrangement wherein the charge in the combustion chamber is stratified so that a homogenous mixture need not fill the combustion chamber in order to have it burn. Stratification is a particularly difficult problem to accomplish in an open chamber engine unless the path of the air flow entering the combustion chamber can be accurately and tightly controlled.
On the other hand, under high speed/high load conditions, it is desirable to have the charge enter the combustion chamber in a relatively unencumbered fashion.
In order to obtain high flow velocities at low speeds, it is necessary to restrict the cross-sectional area of the intake passage. However, such restricted passages seriously and adversely effect the breathing capacity of the engine and reduce its high speed output. In addition, the turbulence generating devices normally used also restrict airflow and adversely effect high speed/high load conditions.
Therefore, induction systems have been proposed which, in effect, are split-type induction systems. That is, the induction system is tuned and sized so as to provide a high speed turbulent airflow at low and mid-range and a larger unrestricted flow under high speed/high load conditions. These goals can be accomplished by utilizing separate inlet passages for each of plural valves in the combustion chamber and controlling the flow so that only one passage primarily serves the combustion chamber at low speeds and at mid-range and both passages serve the combustion chamber at high speed/high load. This type of arrangement generally requires separate independent passages each serving a respective intake port.
In order to achieve stratification and better fuel control, the use of port-type fuel injection is resorted to. However, if a port-type injector is employed and separate intake passages are provided for each intake port of the engine, then multiple fuel injectors may be required. This obviously adds to the cost of the engine.
It is, therefore, a principal object of this invention to provide an improved multi-port intake passage for an engine that permits separate tuning and yet which can operate with a single fuel injector.
The aforenoted techniques for providing split induction systems are particularly advantageous in engines having two intake valves per cylinder. With such arrangements, the intake valves are symmetrically placed and if one intake port has its flow restricted or shutoff, the resulting flow will tend to generate swirl in the combustion chamber which promotes turbulence. However, there are instances when other types of turbulence generating systems are required. Specifically, swirl is a motion of the air in the intake chamber which takes place around the axis of the cylinder bore. However, it has been found that under some running conditions another type of swirling motion is more effective. This type of swirl occurs around an axis that extends transversely to the cylinder bore and is frequently referred to as "tumble."
The advantage of using tumble is that the rate of swirl actually increases as the piston approaches top dead center, at the time approaching ignition, because the swirling path is shorter and hence the velocity becomes higher. Conventional swirl tends to dissipate at this time, however. In addition, this type of motion (tumble) has other advantages over swirl with at least some engines and under at least some running conditions. Tumble is more difficult to achieve in a multi-valve engine.
It is, therefore, a still further object of this invention to provide an improved multi-port, split induction, internal combustion engine wherein tumble can be generated easily.
As has been noted, it is very desirable to use multiple intake valves to improve engine performance particularly at the high speed/high load range. Although two intake valves per cylinder are normally used for this purpose, it has been recognized that the use of three intake valves permits even greater increases in engine performance.
When three intake valves per cylinder are utilized, it is the normal practice to provide one center intake valve that is disposed further from a plane containing a cylinder bore axis with a pair of side intake valves disposed on opposite sides of this center intake valve and close to the plane. In fact and at times, the one or both of the side intake valves may extend over this plane onto the exhaust side of the engine. Such valve placement, however, makes it difficult at times to provide the type of tuning and turbulence previously referred to.
It is, therefore, a principal object to provide an improved induction system for an engine having three intake valves per cylinder.
It is a further object of this invention to provide an improved three intake valve engine wherein the induction system can be tuned to provide optimum running under all conditions.
It is a further object of this invention to provide an improved control arrangement for a three valve per cylinder engine that can achieve the desired degree of turbulence under low speed and low loads and maximum output under high speed/high load conditions.
If three separate intake passages are utilized in a three valve per cylinder engine, then the problems of the number of fuel injectors employed also is present. That is, the problems of this concept are greater with three separate intake passages than with two as should be obvious.
It is, therefore, a still further object of this invention to provide an improved variable tuned, three valve per cylinder engine wherein the number of fuel injectors are minimized and wherein stratification may be obtained if desired.
The placement of the three intake valves as aforedescribed also makes the generation of tumble in the combustion chamber more difficult. In some regards, tumble has more advantages in three intake valve engines than two intake valve engines. However, because the center intake valve is placed further from the plane that passes through the center of the combustion chamber, the center intake valve tends to generate a tumble in the combustion chamber which is counter to the tumble generated by one or both of the side intake valves. Therefore, the actions may conflict with each other and make it difficult to obtain the desired flow patterns under all running conditions.
It is, therefore, a still further object of this invention to provide an improved intake port arrangement for a three valve per cylinder engine wherein each of the intake ports is configured and tuned separately from the others.